A resolver is a rotary transformer used to measure position of a rotating shaft that is mechanically connected to the rotor. A resolver typically includes three magnetically coupled inductors, as shown in FIGS. 1 (a) and 1 (b). A first winding, called the “primary”, may be mounted either in the rotor (FIG. 1 (a)) or on the stator (FIG. 1 (b)). The primary is excited by a sinusoidal voltage signal having the form EXC=Vexc*sin(ωt). A pair of secondary windings is mounted on the stator, magnetically orthogonal to each other. Due to electromagnetic coupling between the primary winding and each of the secondary windings, voltages are induced in the secondary windings having the form Vp*sin(ωt)*sin(θt) and Vp*sin(ωt)*cos(θt) respectively, where θ represents the angular orientation of the rotor and Vp is proportional to Vexc. For this reason, the secondary windings are called the sine channel and cosine channel respectively.
In the case of a variable reluctance resolver (FIG. 1 (b)), an element in the rotor provides the electromagnetic coupling between primary and secondary windings which in turn facilitates both the primary and secondary windings to be located on the stator. Therefore, there are no windings on the rotor as shown in FIG. 1 (b).
A Resolver-to-Digital converter (RDC) is an integrated circuit that measures the analog signals output from the sine and cosine channels of a resolver and generates a digital output code representing the rotor's angular position (θ). Conventionally, the RDC chips are designed to accept a predetermined limited range of voltages for the sine and cosine channel signals received from the resolver. Although the RDC chips are designed to a predetermined range of input voltages, the chips often are coupled to a variety of makes and models of resolvers, which do not always match the RDC's input range. Accordingly, purchasers of mismatched RDC chips and resolvers often must design interface circuits to match the resolver outputs to the RDC inputs. Designing such interface circuits not only can increase the total cost of ownership (TCO) of such resolver systems but it also can induce signal distortions or signal processing delays which can induce errors in the calculated value of θ.
Accordingly, there is a need in the art for an interface system between RDCs and resolvers that dynamically match the input range of the RDC to the output range of a resolver connected to the RDC. Further, there is a need in the art for such an interface system that performs dynamic matching without inducing distortions or propagation delays in the sine or cosine channels output from the resolver.